1. Field of the Invention
An object of the present invention is a method for the creation of animated graphics. It can be used in the cinema and television industries. In these industries, it is useful for the creation of animated graphics for entertainment as well as for professional purposes, for example for training. It is aimed at making the movements performed in pictures by characters and, more generally, by entities more agreeable to the eye and hence more natural. These characters or these entities move about in an environment that shall be called a setting. The setting itself may be animated, i.e. it may change its appearance from one picture to another. The invention is aimed particularly at resolving a problem that arises when the animated entities are made by an operator, called an animation artist or animator while the animated setting is made by another animator or even by the same animator at another time. Putting together these two pictures requires, so to speak, an operation of synchronization that is performed far more simply with the invention than can be done in the prior art. The invention also seeks to give the moving entities behavior that is fluid and not jerky. Finally, the invention has the effect of modifying the postures of the entities from one picture to another, if these postures are not in harmony with the changes of the setting in which they are moving.
The term "setting" shall refer to the set of structures constituting the environment in which a character or an entity is supposed to move. A setting may have several states or appearances. These states are, to put it in a simplified way, the impression that may be had of the setting from a given viewpoint with a given lighting and with a given depth and field width. In the same way, an entity, most frequently a character, could have postures that intrinsically represent different positions of this character in space. A scene is constituted by the association of the picture of a state of the setting (it will always be called a state) with the picture of an posture (hereinafter called a posture). It must be assumed, however, that the notions of setting and entity are reversible, it being possible for the one to replace the other.
In a particular implementation of a method such as this, a state is constituted by a set of (3D) volume elements that correspond or do not correspond to the presence of a structure (such as a tree, house etc.). In a memory of a computer system, it is possible to make memory cells correspond biuniquely with these volume elements, each of said memory cells being loaded with a binary information element (1 or 0) depending on whether or not this memory cell corresponds to the presence of a structure. The information may be different from binary information if the colors are to be depicted: in this case, it may comprise for example three information elements corresponding to red, green or blue for display in television mode. A state as well as a posture are constituted in the same way, by a set of memory cells loaded with information elements 1 or 0.
The assembling of the two pictures to constitute a scene amounts to replacing the information borne in the memory cells corresponding to the setting by an information element corresponding to the entity. Quite simply, when, for the picture of a posture, a memory cell loaded with a zero information element is encountered (implying that there is no character present at this place), the value loaded in the corresponding memory cell of the state is kept. By contrast, as soon as the memory cell corresponding to the character has an information element, this information element is substituted for the information relating to a state. Cases of conflict may arise when, typically, it is sought to place a posture of the character in an impossible place: for example, inside a structure of the setting. It is therefore seen that there is an essential operation that consists, firstly, in securing or fixing the posture with respect to the state and, secondly, in replacing the information elements relating to state by information elements relating to posture.
2. Description of the Prior Art
Until now, despite the development of techniques, the creation of animated sequences has been rather a matter of piecemeal tinkering. It keeps the animators occupied for very lengthy periods of time. For example, it is known that a sequence of a one-minute scene comprising an entity moving in a setting requires work by two animators for one month. With the invention, a sequence such as this requires the work of only one animator for three days. If we look at the problem of the synchronization of the movements of entities in settings, it can even be estimated that the movement of an entity in a setting, for a one-minute sequence, requires fifteen days' work by an animator. With the invention, this problem of movement is resolved in one minute.
The invention relates to the field of 2D graphics as well as to that of 3D graphics. In both cases, the invention relates to animated graphics created with the aid of a computer. For 2D graphics, it can easily be seen that a picture can be represented by a set of picture elements or pixels arranged in matrix form, each carrying an information element on luminance and chrominance. Notably, with digitization, these information elements on luminance and chrominance can be stored in a picture memory of a computer. In correspondence with each pixel of a picture, there is an address of a memory cell of the memory and information elements have been loaded into this cell. It is thus possible to store a 2D picture of the entity as well as a 2D picture of the setting. With a picture of an entity and a picture of a setting, it is possible to constitute a picture of a scene by carrying the entity into the setting. Naturally, the work is done in the memory of the computer by manipulating the addresses and the contents of the concerned cells. If necessary, rather than carrying out a replacement, it is possible to make a composition of the pixels of the setting and of the pixels of the entity at the position of the entity to obtain effects of transparency. All these effects are of a known type.
In the same way, it is possible to define a 3D picture. The term "picture" is used on the understanding that what is represented is a phenomenon, either real or simulated, that occurs throughout the volume of space. To simplify the explanation, it can be assumed that a character will correspond, in space, to volume elements, called voxels, loaded with an information element 1 within the character and 0 outside the character. For all the voxels, it is possible to store an information element 0 and 1 in memory cells of a picture memory. Naturally, rather than having a limit of only one binary information element, it may be preferred, for 2D pictures, to have a more complex information element, notably an information element on chrominance. The setting is defined in the same way, and the scenes are constituted as above by the replacing, in the 3D picture of the setting, of the voxels of the setting by the voxels of the entity.
In another mode of implementation, the entities and the settings are described by a set, that is limited, of characteristic points. The collection of the memorized or stored information elements pertaining to these characteristic points replaces the memorizing or storage of all the points, voxels or pixels, of the scene to be constituted. A memorization or storage system such as this, called a vector system, is less demanding in terms of memorizing or storage capacity and is speedier in terms of image processing. This vector system is preferred from this viewpoint. The constitution of the scenes follows a same procedure as in the previous mode of implementation.
To show 3D pictures, use is made of known types of display methods that make it possible to obtain a rendition of the scene. These display methods, by their principle, simulate the subjecting of the scene to an illumination and simulate the observing of this scene, possibly with an effect of perspective, from a given viewpoint. There are many known techniques that enable this display, notably the so-called OCTREE techniques or again the so-called ray-casting techniques. The invention is not concerned with these display techniques since, in 2D, the invention produces the picture to be displayed directly while, in 3D, the invention can be used to produce the scene which will itself be displayed by these techniques.
The constitution of animated sequences calls for the creation of several pictures. For example, for display in television mode, it is necessary to produce up to 25 pictures per second, giving about 1500 pictures for a one-minute sequence. Rather than having to draw each of these 1500 pictures, both for the setting and for each of the entities, when there are many entities, software programs are used, with a posture of an entity in a first key position at a first key date and a second posture of this entity at a second key date being known, to obtain intermediate postures by interpolation. It may be recalled that, in animation, it is not sought to obtain pictures of real motions but pictures of artificial motions. For example, there is a known software program called "SOFTIMAGE and CREATIVE ENVIRONMENT" by the firm SOFTIMAGE, Montreal, Quebec, Canada, in which a key positioning technique of this kind is implemented. This software furthermore makes use of a library of shapes, generally known as primitives, that are used together to constitute the entities (the characters) or the settings. A software program such as this therefore makes it possible to dispense with the creation of the numerous intermediate pictures needed between the key dates, and reduces the work of the animators accordingly.
To improve a method such as this, in the invention, it is sought firstly to synchronize the moving of the entities with respect to the setting. To attain this goal, the character must be placed accurately in the setting. The principle of the invention is then the following one. For a first scene constituted from a first state of the setting and from a first posture of the entity, a pivot position is identified: this is a place where physically the entity would rest (in the gravitational sense) or would take support on the setting. For example, a character walking, with one foot on the ground, enables a pivot to be obtained: the pivot is this foot. For the same setting, but for a following posture of the character (the next step), this foot of this character is made to take support at the same place of the setting. The other parts of the character then occupy positions, in the space of the scene, that are different from the positions of these same parts for the preceding posture. Then, a second pivot of the second posture of the character is determined. Then a comparison is made of the positions of this second pivot between the first posture and the second posture in the first state of the setting. Then, the place where this pivot should, in turn, take support on the setting is determined. Then the second scene, namely the subsequent scene, is constituted by making this second pivot take support, for the second posture, on this determined place in the setting. This method prevents an abnormal dislocation or lag of the motion of the setting with respect to the motion of the character.
As an improvement, to constitute sequences of intermediate pictures, the invention is not limited to a linear interpolation between positions of characteristic points of the characters. On the contrary, these motions are made more natural by modifying their trajectory. In particular, for a characteristic point of a character, the invention takes account not only of its position in each of the two key postures but also of the speeds at which these characteristic points shift in relation to preceding or following key pictures.
Finally, to make the motions more realistic, a special study is made of the trajectory of the center of gravity of the entity, and it is seen to it that, during all the intermediate pictures that are prepared, this center of gravity follows a curve that has the least possible unevenness. In this case, starting from a given posture and having to reach another given posture, a modification is made, for the intermediate pictures, with an inverted kinematic method, of the form of the posture in such a way as to dampen the shifts of this center of gravity.